When Microsoft and its partners shipped the first Windows Phone 8 handsets last fall, users noticed something disconcerting: Despite the promised backwards compatibility with previous generation Windows Phone 7.x apps, some favorite apps, including Spotify, were not available for the new platform. Over time, however, these apps are reappearing in native Windows Phone 8 guise. And today, a beta version of Spotify is available.

If you’re curious why Spotify and some other key Windows Phone 7.x apps dropped off the face of the earth, at least for Windows Phone 8 users, the reason is simple: They were written with native code, which in Windows Phone 7.x required special assistance and permission from Microsoft. (That’s no longer true in Windows Phone 8.) But since the underlying platform in Windows Phone 7.x was based on Windows CE, and not on mainstream Windows versions, that code isn’t native to Windows Phone 8. So these apps simply won’t run on Windows Phone 8. And Spotify is one of those apps.

The new version of the app, available exclusively on Windows Phone 8, brings the excellent Spotify service back to Microsoft’s mobile platform. If you’re not familiar with Spotify, it’s an online music service, similar in some ways to Pandora or Xbox Music Pass, that lets you listen to radio-like playlists (Pandora-like) as well as selections of songs you’ve carefully crafted (as you might with Xbox Music Pass).

Spotify is available in three tiers. The free version lets you listen on your PC and is ad supported. An Unlimited tier removes the ads for just $4.99 per month. And the high-end Premium tier, which costs $9.99 per month, lets you listen on mobile devices, too, and download songs for offline use.

You need the Spotify Premium subscription to use Spotify on Windows Phone 8. However, Spotify says that “you can try it on your mobile device for 48 hours, completely free. You don’t even need to enter credit card details. Simply download the app and log in.” The Windows Phone Blog claims the free period is 30 days long, however.

According to the firm, Spotify for Windows Phone 8 includes the following features:

Search, browse & play millions of tracks.

Explore & play your friends' playlists, top artists and tracks.

Stream over WiFi or 2.5/3G all your existing playlists are available.

Offline playlists play your music without an internet connection.

On-the-fly sync every track you add to a playlist appears on mobile and computer.

What's New view.

Receive music from friends via the inbox.

Starred tracks tag all your favourites into a special list.

Spotify is among a rare group of gotta-have-it apps for Windows Phone 8, alongside some of my previous app picks like LastPass and Kindle, as well as Audible, as it’s a viable alternative to Xbox Music Pass, which currently only works with Windows 8/RT/7, Windows Phone 7.5/8, and Xbox 360. Spotify is also available on Windows, Mac, iPhone, iPod touch, iPad, and Android devices.